1. Field of the Invention
The present invention generally relates to a rotary channel-selector valve and more particularly, to a rotary channel-selector valve such as a 4-way valve which is applied to a switching mechanism of heating/cooling in a heat pump system and to a structure of a main valve element of the valve.
2. Description of the Related Art
A channel-selector valve wherein a main valve element separates from a valve-seat plate during valve-switching movement by opening or closing a pilot passage penetrating the main valve element in an axial direction has been proposed by the same applicant in Japanese Patent Application Laid-open No.9-292050 (hereinafter "JP '050") as a rotary channel-selector valve wherein a connecting point of a low pressure port provided on a valve-seat plate, fixed to a valve housing and put into contact with an end surface of a main valve element, shifts from one of first and second switching ports on the valve-seat plate to the other one thereof by rotating, in the valve housing, the main valve element, having a high pressure connecting groove and a low pressure connecting groove on the end surface thereof, between first and second channel-switching positions and simultaneously a connecting point of a high pressure port of the valve-seat plate shifts from the other one of the first and second switching ports to the one thereof.
A 4-way valve proposed in JP '050 is superior to a conventional one in the following points. That is, the 4-way valve in JP '050 enables a heat pump system to start cooling or operation in a shorter time after valve-switching movement since a high pressure port and a low pressure port communicates during the valve-switching movement thereby to equalize pressure in both of the pressure ports without stopping a compressor, differing from a conventional rotary channel-selector valve, and further the main valve element can be rotated with smaller force since static friction force at rotation start and also sliding resistance both between the main valve element and the valve-seat plate are smaller due to the separation of the main valve element from the valve-seat plate during the valve-switching movement.
As described above, since the 4-way valve proposed in JP '050 executes the valve switching movement without stopping the compressor, a space is formed between the valve-seat plate and the main valve element separated from the valve-seat plate during the valve-switching movement, and therefore the main valve element is pushed in a direction of separating the main valve element from the valve-seat plate by pressure of a high pressure fluid filled in the space.
Consequently, the main valve element separated from the valve-seat plate should abut against any member in the valve housing and movement of the separation of the main valve element from the valve-seat plate should be limited and the main valve element should be pushed on the member.
Therefore, if the fluid pressure in the space formed between the valve-seat plate and the main valve element separated from the valve-seat plate is too high, the main valve element beginning rotation between the first channel-switching position and the second channel-switching position is forced to stop on the way by contact resistance against the above member limiting the separation movement, thereby causing incomplete rotation of the main valve element.
Moreover, since the high pressure fluid jetting from the high pressure port to the space between the main valve element and the valve-seat plate during the valve-switching movement is not simply directed to the low pressure port and turbulent flow arises by an existence of the high and low pressure connecting grooves formed on the end surface of the main valve element, the main valve element beginning rotation between the first and second channel-switching positions is forced to stop on the way by receiving rotating force opposite to the rotating direction, thereby causing incomplete rotation of the main valve element.
More specifically, the 4-way valve proposed in JP '050 has a structure consisting of the valve housing being in a cylindrical shape; the main valve element provided in the valve housing rotatably and axially movably; the valve-seat plate fixed to the valve housing and having the low pressure port connected to a low pressure piping, the high pressure port connected to a high pressure piping, and at least one switching port; a pilot valve supported by the main valve element by axially movably engaging a valve holding hole formed in the main valve element for selectively connecting the low pressure port to a pressure chamber formed on one end surface side of the main valve element and receiving pressure of the high pressure port by opening or closing a valve port formed on the main valve element; and an electromagnetic solenoid for rotating the main valve element and for opening or closing the pilot valve, wherein the end surface, facing oppositely to the pressure chamber, of the main valve element is put into contact with the valve-seat plate and the main valve element selectively connects the switching port to either one of the low pressure port and the high pressure port by rotation of the main valve element itself.
With respect to the above conventional rotary channel-selector valve of JP '050, since the pilot valve consists integrally of the stem portion engaging the valve holding hole axially movably and attracted by the electromagnetic solenoid and of a needle valve portion to open or close the valve port, a supporting condition of the stem portion by the valve port directly affects radial position or directional position of the needle valve portion relative to the valve port, thereby causing a uncertainty of shutting off the valve port by the needle valve portion.
Especially, in case of providing a communicating passage connecting the valve port and the pressure chamber between the stem portion of the pilot valve and the valve holding hole to receive the stem portion, the stem portion would get rickety, whereby radial position or directional position of the needle valve portion relative to the valve port becomes unstable, thereby making shutoff characteristics of the valve port by the needle valve portion worse.
Further, a concentric machining accuracy between the stem portion and the needle valve portion and also a concentric machining accuracy between the valve holding hole and the valve port also affect shutoff characteristics of the valve port, and accordingly designed shutoff characteristics of the valve port can not be attained without the above machining accuracy being high.
In case that the stem portion of the pilot valve is held by both of the valve housing and the main valve element by means of engagement of the stem portion with a pilot valve guide-tube formed on the valve housing having the electromagnetic solenoid and with the valve holding hole of the main valve element having the valve port, a positioning accuracy of the pilot valve guide-tube formed on the valve housing and an assembling accuracy of the main valve element to the valve housing directly affects radial position or directional position of the needle valve portion relative to the valve port, thereby causing a uncertainty of shutting off the valve port by the needle valve portion.
And, in case that a fixed attractor of the electromagnetic solenoid is provided on the pilot valve guide-tube of the valve housing oppositely to one end of the stem portion of the pilot valve and also a chamber is formed in the pilot valve guide-tube and between the stem portion and the fixed attractor, fluid like a lubricant or a refrigerant would invade the chamber through clearance between the stem portion and the pilot valve guide-tube and stay in the chamber, thereby causing a uncertainty of smooth opening and closing movement of the pilot valve.
Further, with respect to the above rotary channel-selector valve, the electromagnetic coil is fixed to the magnetic pole equipping electromagnetic surface of the valve housing for rotating the main valve element by the magnetic action against a multipolar magnet.
In the above rotary channel-selector valve and the like, since the magnet pole pieces, magnetized by the electromagnetic coil, on the valve housing side rotates the main valve element by the magnetic action against the multipolar magnet on the main valve element side, the magnet pole pieces have to be circumferentially positioned on the valve housing for rotating the main valve element accurately between a predetermined channel-switching positions. To cope with the above, for example, a 4-way valve disclosed in Japanese Patent Application Laid-open No.8-42737 (hereinafter "JP '737") has a positioning projection provided on a body-cap of a body (a valve housing) and simultaneously a concave formed on one end surface, contacting the above body-cap, of a coil bobbin of an electromagnet having an iron core (magnet pole pieces), and then the magnet pole pieces are circumferentially positioned on the valve housing by positioning the electromagnet relatively to the valve housing by means of engagement between the positioning projection on the body-cap and the concave of the coil bobbin.
The above positioning means of the magnet pole pieces of the 4-way valve functions satisfactorily. However, the positioning means would require an improvement for necessity of forming a concave or convex on the coil bobbin, wherein troublesome work of designing a metal mold correspondingly to the concave or convex is required, in comparison with forming a concave or convex on a body side by method of punching or pressing, since the positioning between the body and the coil bobbin is done by direct engagement between them.